Locke understood time through the succession of events in consciousness.
Objection: The explanation is circular since “succession” requires that we have an idea of time already.
Response: Circularity more vitiates proofs than explanations, but in any case Locke’s assumption is not circular since mental succession is not temporal. A syllogism or geometrical proof has premises and conclusions but both are given simultaneously, and by “simultaneously” we don’t mean that the proof itself has a temporal dimension. You may have seen all the steps of the argument simultaneously in 2003 but this does not make 2003 a feature of the argument. What is true of inference is also true of narratives, since a thing can’t happen all at once but in order to be a narrative it has to be seen all at once. It’s impossible to see, say, the parable of the prodigal son as a story of forgiveness unless the story is seen as a whole, and it’s meaningless to speak of a structure or point of a narrative apart from a wholeness that cannot be given in the temporal events themselves.
The Broader Theory:
And so we have to make some sort of distinction between the temporal and mental world where the temporal world has succession with time whereas the mental world has succession without time. The mental world is capable of a sort of wholeness that the temporal world is not, and we can call this wholeness “simultaneous” possession which is not the simultaneity of events in time. The temporal world lacks this wholeness because it requires intermediate stages of existence between intelligible terms, and these intermediate stages exclude the co-existence that characterizes the succession of the mental world. As just argued, these intermediate stages between intelligible forms is time properly speaking, which makes the wholeness of rational-narrative co-existence impossible. In the sense of existence that is proportional to fullness or wholeness, the temporal world exists less than the rational-narrative world.
But this relation of higher and lower modalities of existence is a lesson in all existence relations. The higher serves, illumines, and discloses the lower. The temporal world cannot exist all at once but the simultaneity of thought nevertheless discloses it as it is. While the higher takes things in from the lower (as is articulated in theories of abstraction or recollection) the lower takes far more from the higher since it borrows the wholeness that its temporarily excludes from it.